[#llvm-RecurrenceDescriptor-isReductionPHI]
= xref:llvm.adoc[llvm]::xref:llvm/RecurrenceDescriptor.adoc[RecurrenceDescriptor]::isReductionPHI
:relfileprefix: ../../
:mrdocs:

Return true if `Phi` is a reduction PHI in `TheLoop.`

== Synopsis

Declared in `<llvm/Analysis/IVDescriptors.h>`

[source,cpp,subs="verbatim,replacements,macros,-callouts"]
----
static
bool
isReductionPHI(
    xref:llvm/PHINode.adoc[PHINode]* Phi,
    xref:llvm/Loop.adoc[Loop]* TheLoop,
    xref:llvm/RecurrenceDescriptor.adoc[RecurrenceDescriptor]& RedDes,
    xref:llvm/DemandedBits.adoc[DemandedBits]* DB = nullptr,
    xref:llvm/AssumptionCache.adoc[AssumptionCache]* AC = nullptr,
    xref:llvm/DominatorTree.adoc[DominatorTree]* DT = nullptr,
    xref:llvm/ScalarEvolution.adoc[ScalarEvolution]* SE = nullptr);
----

== Description

Returns true if Phi is a reduction in TheLoop. The RecurrenceDescriptor is returned in RedDes. If either `DB` is non‐null or `AC` and `DT` are non‐null, the minimal bit width needed to compute the reduction will be computed. If `SE` is non‐null, store instructions to loop invariant addresses are processed.

== Return Value

True if `Phi` is a reduction PHI in `TheLoop.`

== Parameters

[cols="1,4"]
|===
| Name| Description
| *Phi*
| PHI node to test as a reduction.
| *TheLoop*
| Loop containing `Phi.`
| *RedDes*
| Descriptor filled when `Phi` is a reduction.
| *DB*
| Optional DemandedBits analysis for bit‐width computation.
| *AC*
| Optional AssumptionCache for bit‐width computation.
| *DT*
| Optional DominatorTree for bit‐width computation.
| *SE*
| Optional ScalarEvolution used when processing invariant stores.
|===


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